This section is intended to provide background information to facilitate a better understanding of various technologies described herein. As the section's title implies, this is a discussion of related art. That such art is related in no way implies that it is prior art. The related art may or may not be prior art. It should therefore be understood that the statements in this section are to be read in this light, and not as admissions of prior art.
Seismic surveys can be conducted at sea, on shore, or in zones between sea and shore, e.g. in shallow bays, in swampy areas, and the like. A common feature of the surveys is that a seismic signal is transmitted from a seismic source and this signal is reflected by a ground formation and proceeds to be intercepted by seismic sensors. The seismic signals are then transmitted to an appropriate receiver station, where the data are processed, stored, and used for constructing structural maps of the rock formations. These maps facilitate the process of assessing the probability of the existence of oil or gas in the surveyed area.
In marine surveys, where it is the seabed that has to be surveyed, a typical seismic tow will consist of one or more sources and one or more cables, also called streamers. The actual towing is performed by one or more vessels. The seismic equipment towed behind the vessels is usually submerged in the water. A streamer generally extends to a length ranging from a few hundred meters to several thousand meters. Inside the streamer, there are located a large number of sensors, such as hydrophones and geophones. A source usually consists of several suitable sonic guns, for example, air guns, which are arranged in a row or in a group. This is also called a gun array. When air guns are used, the guns are filled with compressed air, which is then released, thereby forming the seismic pulse. This is also called a seismic shot, or a shot point. It is this pulse, which, after having been reflected, is intercepted by sensors in the seismic streamer.